Keggin heteropolyacid-based catalysts for the preparation of substituted ethyl β-arylaminocrotonates, intermediates in the synthesis of 4-quinolones

Catalysts based on tungstophosphoric and molybdophosphoric acids supported on SiMCM-41 and amine-functionalized SiMCM-41 were obtained. They were characterized by FT-IR and 31P NMR spectroscopies, and their acidity was determined by potentiometric titration with n-butylamine. The undegraded Keggin structure was observed when the heteropolyacids (HPA) are supported on SiMCM-41, and there was a partial degradation to a lacunar species on the amine-functionalized carrier. Also, the acidity of the latter catalysts was lower. The supported Keggin heteropolyacid catalysts are used for the preparation of different substituted ethyl β-arylaminocrotonates, intermediates in the synthesis of 4-quinolones, from substituted anilines and ethyl acetoacetate. The products were obtained with high selectivity. The effect of the different nature of the aniline substitutes was observed. For this Conrad–Limpach reaction, the activity of the prepared catalysts agrees with the different characteristics of the supported heteropolyacids, the yield being higher for the SiMCM-41 supported catalysts.